The file has the same base name as the source file and an .i extension. In the process, all preprocessor directives are carried out, macro expansions are performed, and comments are removed. To preserve comments in the preprocessed output, use the /C (Preserve Comments During Preprocessing) option along with /P.

/P adds #line directives to the output, at the beginning and end of each included file and around lines removed by preprocessor directives for conditional compilation. These directives renumber the lines of the preprocessed file. As a result, errors generated during later stages of processing refer to the line numbers of the original source file rather than lines in the preprocessed file. To suppress the generation of #line directives, use /EP (Preprocess to stdout Without #line Directives) as well as /P.